Authentication articles such as cash cards, credit card and passports, and valuable securities such as gift certificates and stock certificates are desired to be difficult to counterfeit. Conventionally, labels are attached on those articles to prevent their counterfeiting or imitation and to facilitate distinguishing them from counterfeit products or imitation products.
Further, in recent years, there is a problem that counterfeits of other products than authentication articles and valuable securities are also in the market. Accordingly, anti-counterfeiting techniques as described above for authentication articles and valuable securities have been more often applied to such products.
As an example of anti-counterfeiting techniques, an anti-counterfeit medium which is a polarized latent image device having a retardation layer formed on a reflection layer has been proposed. When observed via a polarized light film, the anti-counterfeit medium shows an image with clearness continuously varying depending on an angle formed by the polarization axis of the polarized light film and a slow axis of the retardation layer.
For example, the anti-counterfeit medium disclosed in PTL 1 divides each of the first identification data and the second identification data into a plurality of partial images, and provides a plurality of transparent areas which corresponds to the plurality of partial images which are disposed adjacent to each other in a same plane so as to form the retardation layer, the plurality of transparent areas having optical axes which are oriented in different directions from each other in a rotation direction. With this configuration, a plurality of latent images which are recorded to be overlapped each other can be individually observed with high contrast ratio.